Allow use of :path_prefix and :name_prefix outside of namespaced routes

The :path_prefix and :name_prefix options are supported almost correctly on all routes, but they are only removed from the options hash in divide_route_options if the :namespace option is set, which interferes with route generation (i.e. the :path_prefix must be supplied in order for the route to match).

This is a shame since it would be convenient to use with_options to supply a common :path_prefix to a bunch of routes.

Attached is a tiny patch to always discard the :path_prefix and :name_prefix options, not just when a namespace is in effect.